FWIW, not all encoding has to do with IO, and there is an X::Encoding
namespace already... it should probably go there.
This particular error occurs in the VM (at least on rakudo-m). Currently
exception passing from MoarVM is limited to a single type of exception.
Supposedly there's to be a mechanism to register an alternate
VMException-compatible HLL object but I don't see that from reading the
code... the one in boot_types seems to be used everywhere.
I'd say it's better to wait for that Moar work, or a decision not to do
that, than to start tearing into the text of VMException contents and
trying to figure out what other exception to wrap it in other than an
X::AdHoc.
In certain cases we can immediately catch exceptions from the VM
in wrapper functions around an NQP call. If the VM would let us
build a different exception in that handler and attach it to the
HLL-registered exception and rethrow it, then the exception handler
could detect that and the next time it emerges, maybe some slight
of hand could make that new exception take the place of the original
while keeping backtraces intact.
I only mention that because it is a way we could keep the code that
examines VM exceptions and maps them to HLL exception types local
to the relevant code in both the HLL and in MoarVM, so we don't
have to have big switch statements and consider some sort of centralized
registry in MoarVM to keep two unrelated VM exceptions from clashing
and becoming indistinguishable to the HLL.
I played a bit with that but it looks like trying to change the
BOOTException payload doesn't happen, though you can change its message:
perl6 -e 'use nqp; sub f { "dh°".encode("ascii"); CATCH { when X::AdHoc { my \xp = nqp::getattr($_, Exception, "\$\!ex"); nqp::setmessage(xp, nqp::decont("foo")); nqp::setpayload(xp, nqp::decont(X::NYI.new())); $_.rethrow } } }; f(); CATCH { ":: {$_.perl} { my \xp = nqp::getattr($_, Exception, "\$\!ex"); my \xpp = nqp::getpayload(xp); xpp.^name } ::".say }'
:: X::AdHoc.new(payload => "Error encoding ASCII string: could not encode codepoint 176") X::AdHoc ::
foo
in sub f at -e line 1
in block <unit> at -e line 1
...that would have required some further alterations to EXCEPTION to detect
the changed payload, even if setting the payload had worked.
Or maybe it did work and EXCEPTION undid it...